Many Military U.F.O. Reports Are Just Foreign Spying or Airborne Trash

WASHINGTON — Government officials believe that surveillance operations by foreign powers and weather balloons or other airborne clutter explain most recent incidents of unidentified aerial phenomenon — government-speak for U.F.O.s — as well as many episodes in past years.

The sightings have puzzled the Pentagon and intelligence agencies for years, fueling theories about visiting space aliens and spying by a hostile nation using advanced technology. But government officials say many of the incidents have far more ordinary explanations.

Intelligence agencies are set to deliver a classified document to Congress by Monday updating a report made public last year that said nearly all of the incidents remain unexplained. The original document looked at 144 incidents between 2004 and 2021 that were reported by U.S. government sources, mostly American military personnel.

This article is based on interviews with American officials familiar with the findings of the Pentagon and intelligence agencies’ examination of the incidents. The officials spoke on the condition of anonymity to discuss the classified work.

Some of the incidents have been formally attributed to Chinese surveillance — with relatively ordinary drone technology — and others are also thought to be connected to Beijing. China, which has stolen plans for advanced fighter planes, wants to learn more about how the United States trains its military pilots, according to American officials.

Much of the information about the unidentified phenomena remains classified. While Congress has been briefed on some of the conclusions about foreign surveillance, Pentagon officials have kept most of the work secret — in large measure because they do not want China or other countries to know that their efforts to spy on the American military were detected.

But such official secrecy comes at a cost, allowing conspiracy theories about government lies to thrive unchecked.

Sue Gough, a Defense Department spokeswoman, said the Pentagon remains committed to principles of openness but must balance that with its “its obligation to protect sensitive information, sources and methods.”

While the Pentagon will not “rush to conclusions in our analysis,” Ms. Gough said, no single explanation addresses the majority of unidentified aerial phenomenon reports.

“We are collecting as much data as we can, following the data where it leads and will share our findings whenever possible,” she said.